The development of a robust light source that emits one photon at a time will enable new technologies such as perfectly secure communication via quantum cryptography. Devices based on fluorescent dye molecules, quantum dots, and carbon nanotubes have been demonstrated, but in general these devices do not combine a high single photon flux with stable, room-temperature operation. Luminescent centers in diamond have recently emerged as a candidate for these applications.
Color centers based on Nitrogen, Silicon, Carbon, Nickel, and Chromium impurities have all been demonstrated to emit single photons at room temperature. The Nitrogen-vacancy (NV) center possesses additional electron and nuclear spin degrees of freedom with a long coherence time. NV centers can thus act as a quantum memory for long distance quantum communications, quantum computing, and nanoscale magnetometry. Light-matter interactions, and in particular in- and out-coupling of photons, can be engineered by embedding emitters such as a Nitrogen-vacancy (NV) center within nanophotonic structures. One approach to such coupling is to evanescently couple a separate optical cavity or a waveguide to a proximal NV center. Another approach is to realize optical structures directly in thin diamond films grown on foreign (low-index or sacrificial) substrates, such as polycrystalline diamond films. Devices such as planar photonic crystals or microdisk resonators may also be sculpted from a bulk diamond crystal.